1. Field of the Invention
The present invention relates to a sealing structure of a ball bearing and more particularly to a sealing structure of a ball bearing wherein a seal or a shield is provided on at least one side of the ball bearing to further improve the sealing performance.
2. Description of the Prior Art
Conventional ball bearings, a type of roller bearing, include shield ball bearings, wherein a shield formed of a stainless steel plate is provided on a side of the bearing, and a seal ball bearing wherein a seal formed of a material such as synthetic rubber, thermoplastic resin or elastomer is provided on a side of the bearing.
In the shield ball bearing, invasion of foreign matter or dust into the bearing is prevented, and in the case where grease is sealed in the interior of the bearing, leakage of the grease to the exterior is prevented. In the seal ball bearing, sealing is enhanced to a greater extent than in a shield ball bearing, and the invasion of foreign matter or dust into the bearing and the leakage of grease from the bearing are prevented more effectively.
Generally, such a shield or seal is fixed to an outer ring of the ball bearing. Both a singe shield (seal) type with the shield (seal) provided on only one side of the bearing and a double shield (seal) type with the shield (seal) provided on both sides of the bearing are available. Usually, the shield is provided on an outer ring and spaced from an inner ring so as to define a slight gap therebetween. The sealed ball bearings include a non-contact type wherein the seal does not contact the inner ring and a contact type wherein the seal is in contact with the inner ring.
For all structures and types of ball bearings, applications requiring higher sealing performance have recently been increasing.
For example, in a conventional vacuum cleaner 010 which is one example of application of a ball bearing provided with a seal or a shield, as shown in FIG. 5, high-pressure air present in a fan-driving motor chamber 012, which also serves as a discharge chamber, may flow in reverse into fan chamber 011 through a ball bearing 014 mounted in a partition wall 013 which separates the fan chamber 011 from the motor chamber 012. In FIG. 5, a streamline A represents normal air flow, while a streamline B represents the reverse flow of air into the fan chamber 011. When such a phenomenon occurs, the power consumption of motor 015 increases and the efficiency of the device using the ball bearing is reduced; moreover, grease sealed in the ball bearing 014 leaks out, resulting in burnout of the bearing and shortening life of the device.
Likewise, in a motor-driven tool 020 which is another example of application of a ball bearing, as shown in FIG. 6, grease present in a gear chamber 024 may leak into motor-fan chamber 023, accommodating both a drive motor 021 and a motor cooling fan 022, through a ball bearing 026 mounted in a wall of gear box 025, defining the gear chamber 024 and partitioning the motor-fan chamber 023 and the gear chamber 024. This is because the grease present in the gear chamber 024 is sucked into the motor-fan chamber 023 through the ball bearing 026 by virtue of a negative pressure present at a central portion of the fan 022. The occurrence of such a phenomenon not only reduces the meshing efficiency of gears disposed within the gear box 025 but also results in burnout of gears and shortening the life of the device.
The same phenomenon can occur also in the case where a bearing of a rotary shaft of an impeller is exposed to a high-pressure fluid on the discharge side in a blower where the difference in pressure between the suction side and the discharge side is large.
In such applications as referred to above, it has come to be more and more demanded that the ball bearing be capable of preventing flow or leakage of air or grease through spaces defined on both sides of the ball bearing or capable of preventing grease sealed in the ball bearing itself from leaking out to a lower-pressure space located on one side of the ball bearing.
The present invention has been designed for solving the abovementioned problems associated with the conventional ball bearing sealing structure and it is an object of the present invention to provide a ball bearing sealing structure capable of effectively preventing, with a simple structure, flow or leakage of fluid through spaces formed on both sides of the ball bearing, also capable of effectively preventing grease sealed in the ball bearing itself from leaking into a lower-pressure space on one side of the ball bearing, and thus providing improved sealing performance.
In a first aspect of the present invention there is provided a sealing structure of a ball bearing wherein a seal or a shield is provided on at least one side of the ball bearing and the ball bearing allows rotation of an outer ring, characterized in that a large number of blades project radially from an outer surface of the seal or the shield provided on one side of the ball bearing.
Upon rotation of the outer ring, the seal or the shield rotates together with the outer ring, and the blade projections formed on the outer surface of the seal or the shield cause fluid which is in contact with the said outer surface to be moved radially outward by centrifugal force in an apparatus in which the ball bearing is applied. The blade projections exhibit a pumping action on the fluid which is in contact with the outer surface of the seal or the shield.
The ball bearing is disposed so that the side with the blade projections on the seal or shield faces the space with the higher pressure, whereby fluid present near the inner ring flows radially outward in the space with the higher pressure, resulting in a drop in pressure within this region and in a decrease or reversal of the pressure difference of fluids near and on opposing sides of the inner ring.
As a result, undesirable flow or leakage of fluid from the space with higher pressure to the space with lower pressure, through the ball bearing, is suppressed, permitting the ball bearing to exhibit enhanced sealing performance. Besides, the leakage of fluid (grease) sealed in the ball bearing to the lower-pressure space is suppressed.
In a second aspect, the present invention provides a sealing structure of a ball bearing wherein a seal or a shield is provided on at least one side of the ball bearing and the ball bearing allows rotation of an inner ring. Here also, a large number of blade projections extend radially on an outer surface of the seal or the shield provided on one side of the ball bearing, and an annular plate is mounted on a shaft with the inner ring fitted thereon at a position relatively close to the blade projections.
As the inner ring rotates, the annular plate rotates together with the inner ring through the shaft. Due to this rotation, in a device incorporating the ball bearing, fluid which is present in the region between the annular plate and the ball bearing is pulled by viscous force so as to rotate together with the annular plate. Therefore, the fluid present in the said region rotates relative to the blade projections and the blade projections cause the fluid present in this region and in contact with the said outer surface to flow radially outward by centrifugal force. Thus, the blade projections pump the fluid which is in contact with the outer surface of the seal or the shield.
The ball bearing is disposed so that its one side with the blade projections formed on the seal or shield faces the space on the side having the higher pressure, whereby the fluid present around the inner ring is caused to flow radially outward, with the result that the pressure of the fluid in this region (the region near the inner ring and between the annular plate and the ball bearing) drops and the difference in pressure between fluids present near and on opposing sides of the inner ring decreases or reverses.
As a result, undesirable flow or leakage of fluid from the higher-pressure space to the lower-pressure space through the ball bearing is suppressed and the seal provided by the ball bearing is enhanced. Moreover, leakage of fluid (grease) sealed in the ball bearing to the lower-pressure space is greatly decreased, whereby the seal provided by the ball bearing is enhanced.
In a third aspect of the present invention, a plurality of through holes are formed circumferentially on or near an inner peripheral edge of the annular plate. According to this configuration, in the region near the inner ring between the annular plate and the ball bearing the fluid pressure drops, and high-pressure fluid constantly flows through the plural through holes into that region of lower pressure from the higher-pressure space on the opposite side of the annular plate. Therefore, a circulation path is established, which path is free of reversal of flow of the fluid which undergoes the pumping action and the pumping action of the blades proceeds smoothly.